1. Filed of the Invention
This invention relates to a micro-mechanical device, a micro-switch, a variable capacitor, a high frequency circuit and an optical switch, and more particularly relates to a micro-mechanical device, a micro-switch, a variable capacitor, a high frequency circuit and an optical switch, all of which include piezoelectric actuators made of piezoelectric thin films.
2. Description of the Related Art
There are thin-film actuators which are manufactured as micro-mechanical devices using the micro-electro-mechanical system (MEMS). Micro-switches, variable capacitors and so on including thin-film actuators are activated by electrostatic force. Specifically, driving force is applied to a pair of electrodes which are positioned with a space, so that electrostatic force is generated in order to activate the electrodes.
A voltage of several ten volts is required to displace such electro-static switches in order to accomplish mechanical switching. For instance, since a power supply of 5V or less is used for a cellular phone, a step-up transformer is necessary for the purpose of obtaining a power voltage of several ten volts. Therefore, there is a problem that the power supply has to be enlarged, and becomes very expensive.
In order to overcome the foregoing problem, there has been proposed a thin-film actuator in which cantilevers are displaced by piezoelectric strain (refer to Japanese Patent Laid-Open Publication No. 2000-348,594). With this actuator, displacement necessary for switching can be accomplished by applying a voltage of several volts compared with the electrostatic switch.
A movable distance of a piezoelectric thin-film actuator is proportional to a square of length of its cantilevers while driving force thereof is inversely proportional to a square of the length of the cantilevers. The longer the cantilevers, the smaller the driving force. If an electrode at a free end of the cantilevers and an electrode on a front surface of a substrate are in firm contact with each other, it is very difficult to produce driving force to separate them. This will lead to a malfunction of the thin-film actuator.
The present invention has been contemplated in order to overcome the foregoing problem of the related art, and is intended to provide a micro-mechanical device, a micro-switch, a variable capacitor, a high frequency circuit, and an optical switch.